A tunnel boring machine (“TBM”) is a tunnel excavation apparatus for forming tunnels in a variety of soil and rock strata. A conventional TBM produces a smooth circular tunnel wall, with minimal collateral disturbance. As discussed in U.S. Pat. No. 8,172,334, to Lindbergh et al., which is hereby incorporated by reference in its entirety, a conventional TBM typically includes a full face rotatably driven cutter head that supports a plurality of cutter assemblies. Typically, a cutter head may have 20, 50, 100, or more cutter assemblies rotatably mounted to the cutter head.
A breakthrough that made TBMs efficient and reliable was the invention of the rotating cutter head, developed by James S. Robbins. Initially, Robbins' TBM used rigid spikes rotating in a circular motion, but the spikes would frequently break. He discovered that by replacing these grinding spikes with longer lasting, rotatable cutter assemblies this problem was significantly reduced. Since then, modern TBMs include rotatable cutter assemblies.
In operation, the cutter head is urged against a surface to be bored such that at least some of the cutter assemblies forcibly engage the surface. In some TBMs a plurality of opposing sets of hydraulic cylinders engage the tunnel walls to anchor the TBM, and separate thrust cylinders press the cutter head against the rock or ground surface. The cutter head rotates about a longitudinal axis so that as the cutter assemblies are forcibly pressed against the surface they roll along the surface to fracture, loosen, grind, dislodge, and/or break materials from the surface.
As illustrated in Lindbergh et al., rotatable cutter assemblies are mounted in housings in the TBM cutter head such that the cutter ring extends forward from the face of the cutter head to engage the earthen rock wall. During operation of a TBM the cutter head is pressed with great force against the rock face, typically with hydraulic actuators, while the cutter head is rotated about its axis. The end of the cutter ring of the cutter assemblies engages the tunnel face and produces local stresses that cause the surface of the wall to fracture and crumble. The fractured and loosened material is collected and removed to gradually form the tunnel.
The cutter head and the cutter assemblies are subjected to very high forces during tunnel boring operations. Once excavation of the tunnel is started, it is very difficult to repair or replace the cutter assemblies because the assemblies are difficult to access in situ, and the cutter assemblies are heavy, often weighing many hundreds of pounds. Tunnels are often at significant depths, with correspondingly high ambient pressures. Therefore, it is critical that the installation of the cutter assembly in the cutter head be very secure and reliable, even under the extreme conditions associated with tunnel boring.
FIG. 1 herein shows an exploded view of a conventional cutter ring assembly 10 housing for a tunnel boring machine. The cutter ring assembly 10 comprises a cutter ring 15 disposed on a hub 12 that is rotatably mounted on a shaft 13 for rotation about axis 14. Bearing assemblies (not shown) are mounted generally on the shaft 13 to provide for rotation of the hub 12 and cutter ring 15 about the shaft 13.
The cutter housing assembly shown in FIG. 1 comprises spaced-apart housing mounts 20L, 20R. The rotation axis 14 for the cutter ring 15 is generally perpendicular to the housing mounts 20L, 20R. Opposite ends of the shaft 13 are secured in the housing mounts 20L, 20R in L-shaped channels 21 that are sized to receive the cutter assembly shaft 13. Typically the cutter assembly 10 is installed by positioning the opposite ends of the shaft 13 at the back of the housing mounts 20L, 20R to engage the long leg 21A of the L-shaped channels 21. The cutter assembly 10 is slid along the long leg 21A of the L-shaped channel 21 and then shifted laterally into the recess formed by the shorter leg 21B of the L-shaped channels 21. The cutter housing secures the cutter assembly 10 to the housing mounts 20L, 20R with a pair of wedge-lock assemblies 22A that engage respective ends of the shaft 13.
The wedge-lock assemblies 22A each include a wedge 22, a clamp block 24, and an optional tubular sleeve 28 disposed there between. The wedge 22 is positioned to abut an angled face on the end of the shaft 13, and the clamp block 24 engages abutment surfaces 25 on the associated housing mount 20L, 20R. A bolt 23 extends through the wedge 22, the sleeve 28, and the clamp block 24, and is secured with two nuts 26 and a washer 27. As the bolt 23 is tensioned by torquing the nuts 26 to a design specification, the wedge 22 locks the cutter assembly 10 in place.
In practice, this mounting has presented certain challenges and disadvantages. For example, the housing mounts 20L, 20R are typically hard mounted onto the TBM, for example, by welding or the like. The housing mounts are therefore challenging to remove and replace if they become damaged. If a housing mount becomes damaged, it typically must be replaced in situ, which is particularly difficult and may shut down the TBM for an extended period of time.